The energy industry has depended solely on fossil fuels, but it is now shifting investment to develop new cheaper and cleaner energy sources not related to fossil fuels. Over the past two decades, renewable energy resources have been the focus for researchers, and many different power converters have been designed to make the integration of these types of systems into a distribution grid. As the power grid evolves, there will be more distributed power sources that are configured into microgrids. Microgrids operate with both utility (power network) and renewable power sources (solar, wind, battery, and/or other) with numerous various loads (single and three-phase). Medium, high, and extra high voltage electronic systems are needed to manage and control power flow as well as to assure power distribution quality in transmission lines such as applications for reactive power (“VAR”) compensators, voltage/frequency regulators, solid-state transformers (“SST”), solid-state power substations (“SSPS”), medium and high voltage direct current (“MVDC”/“HVDC”) drives, medium voltage alternate current drives (“MVD”), and others. Therefore, power electronic converters with these capabilities have the responsibility to carry out these tasks with high resiliency and efficiency. The increase in the world energy demands has necessitated the appearance of new power converter topologies and new semiconductor technology.
Electrical power networks produce and use real/active and imaginary/stored power. Typically, power lines carry active power (“KW”) and reactive power (“VAR”). The content of active and reactive power is expressed in power factor. As the total power flows through the line, both active and reactive power compete for capacity. VAR compensation is defined as the management of reactive power to improve the performance of alternate current (“AC”) power networks. The concept of VAR compensation embraces a wide and diverse field of both system and customer problems, especially related with power quality issues, since most power quality problems can be attenuated or solved with an adequate control of reactive power. In general, the problem of reactive power compensation is viewed from two aspects: load compensation and voltage support. In load compensation, the objectives are to increase the value of the network power factor, to balance the real power drawn from the AC supply, to compensate voltage regulation, and to eliminate current harmonic components produced by large and fluctuating nonlinear industrial loads. Voltage support is generally required to reduce voltage fluctuation at a given terminal of a transmission line. Reactive power compensation in transmission networks also improves the stability of the AC network by increasing the maximum active power that can be transmitted. It also helps to minimize variation at all levels of power transmission, it improves HVDC conversion terminal performance, increases transmission efficiency, controls steady-state and temporary over-voltages, and can avoid disastrous blackouts. VAR compensator systems can be electromechanical or static (“SVC”) and can be series or shunt reactive compensators. Series and shunt VAR compensation are used to modify the natural electrical characteristics of AC power networks. Series compensation modifies the transmission or distribution network parameters, while shunt compensation changes the equivalent impedance of the load. In both cases, the reactive power that flows through the network can be effectively controlled, improving the performance of the overall AC power network.
Conventional multi-level cascaded power management systems use a large three-phase 60 Hz transformer with multiple electrically isolated three-phase secondaries which may be phase shifted. These conventional systems supply power to electronic assemblies that convert the 60 Hz power feeding to a variable frequency (0 to 120 Hz) and voltage output. Each output may be implemented with an H-bridge and because these outputs are electrically isolated by the large 60 Hz transformer with isolated secondaries, the H-bridges can be connected in series or parallel. However, there is a need for more efficient systems over these existing Cascaded H-Bridge (“CHB”) topology.
CHB solutions are costly, complex, and unreliable because the designs are limited in switching frequency, dielectric, and thermal capability as well as requiring complicated hardware and cable assemblies. Traditionally, utilities avoid power electronic products due to cost, complexity, and lack of resiliency. In addition, these power electronic products require extra cost for installation because they are designed for operating in clean controlled environments. Within industry, many large motor applications would benefit from using power factor correction on constant speed motors, to save energy through VAR support, but most motor applications do not use power electronic solutions due to cost and reliability concerns. Due to renewable energy and the need for greater network resiliency, new electrical networks are emerging with multiple distributed energy sources rather than few large sources. The need for more flexible and efficient power flow control within a multi-source environment is well documented.
It is with respect to these and other considerations that the disclosure made herein is presented.